The Channel Fracturing Technique Improves Tight Reservoir Potential in the Ordos Basin, China

Abstract

The Ordos basin, located in northwest China, has large known hydrocarbon reserves that represent unique reservoir challenges and require specific operational, logistical, and technical expertise. One of the immediate objectives for PetroChina Changqing is to exploit these low-permeability oil and gas sandstones of the Yanchang formation, and this is done through both vertical and horizontal wells types that include single-stage and multistage hydraulic fracturing treatments. Historically, individual well productivity has been impacted by complex reservoir dynamics, uncertain subsurface properties, and identifying those areas where critical geological and reservoir factors exist in order to generate substantial production. However, most hydraulic fracturing treatments result in low production rates due to reservoir pressure being below the hydrostatic pressure gradient. Therefore, principal fracturing challenges include trying to engineer a highly conductive flow path that depends on fluid viscosity and stability to build geometry and transport proppant toward the fracture tip, while rapidly returning to the base-fluid viscosity to be flowed back. Since reduced fracture conductivity and length were detrimental to well performance, a hydraulic fracturing technique that incorporates the creation of channels within the fracture was deployed. This technology optimized reservoir inflow performance through a specified engineering workflow that requires specific equipment and pumping controls with fluid and fiber technologies. These channels created infinite-conductivity paths for fluid to flow from the reservoir to the wellbore, resulting in higher well productivity. The deployment and application of this technology included 65 treatments performed on five vertical and five horizontal wells in oil blocks and two vertical wells in a gas block. Production performance for all oil wells treated with the flow-channel fracturing technique had initial production index figures being 2.4 times the field average and those wells continue to be upper performers when compared to 180-day accumulated production figures. For the gas wells, 4 to 5 times initial gas production rate was achieved when compared to the average offset wells. In all well cases, channel fracturing increased operational efficiency while resulting in no screenouts.

DEM-CFD Modeling of Proppant Pillar Deformation and Stability during the Fracturing Fluid Flowback

“…As a result, the conductivities measured in the numerical models could be largely dropped due to the occupancy of particles in the fluid channels. The field tests with channel fracturing shows the increase of oil/gas production [3][4][5] compared with the traditional proppant placement scheme, but the improvement is much less remarkable than the experimental results by Gillard et al [1] and Nguyen et al [31]. Due to the flowback of proppant particles, the proppant particles move into the channels between pillars, which results in the single layer or a few layers of proppant particles between pillars (Figure 21).…”

“…It can be seen that when the pressure boundary condition is used, the amount of flowback particles and the spreading area decreases with the increase of fluid viscosity. According to (5), with the constant pressure gradient, increase of the fluid viscosity causes the decrease of the velocity difference v j − u j . However, from (3), the size of the β int j is difficult to determine (one part of (3) increases and the other decreases).…”

“…The oil production with channel fracturing could also be greatly enhanced. For instance, the channel-fracturing operation of tight oil and gas reservoirs in Ordos Basin, China, has produced 2.4 times as much oil as conventional fracturing, and the gas well production is 4-5 times as high as that of conventional fracturing [5].…”

“…The bonding strength of fibers could effectively glue the proppant particle together, and thus, the fiber-proppant cluster is able to better support the hydraulic fractures, prevent the proppant flowback, and also reduce the risk of sanding. In the channel-fracturing tests of Eagle Ford and other shale fields, sand production was improved and fibers showed better proppant flowback resistance [5,8,9].…”

Modeling of Fracture Width and Conductivity in Channel Fracturing With Nonlinear Proppant-Pillar Deformation

“…A production increase of 29% was reported after applying channel-fracturing stimulation in Taylakovskoe Field in Siberia (Valiullin et al 2015). Li et al (2015a) reported stimulation results for channel fracturing in tight oil and gas reservoirs in Ordos Basin, China; the production of oil wells increased by 1.4 times and gas-well production increased by three to five times.…”